Date

2020-11-23

Author

Erkmen, Berrak

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Carbon Fabric-Reinforced Polymers (CFRPs) attract attention due to their high mechanical properties, electrical conductivity, and providing weight reduction solutions in aerospace, automotive, marine, and energy industries. Since recycling, long processing times, non-visible damages, and complex repair procedures of thermoset-based CFRPs cause problems, studies are performed on the application of thermoplastic-based CFRPs. This study aims to produce polystyrene (PS)-based and carbon nanotubes (CNTs) and carbon fabric (CF)-reinforced multilayer composites and to improve their multifunctional properties by applying modifications to PS, CNTs, and CF. The thesis consists of six parts. In the first part, CNTs were modified with surfactants, silane coupling agents, and a copolymer to disperse them homogeneously in the polymer matrix. The suspension stability of the modified CNTs in PS/toluene solution was investigated. Then, PS-CNTs binary composites were produced at different melt mixing conditions and characterized by optical microscope, electrical resistivity measurements, tensile and impact tests. Poly[styrene-b-(ethylene-co-butylene)-b-styrene] grafted with maleic anhydride (SEBS-g-MA) elastomer was also added to selected binary composites to improve the processability and create a soft segment in the structure. PS-SEBS-gMA-CNTs were characterized in terms of morphology, electrical, mechanical, and shape memory properties. Results revealed that H2SO4-HNO3 solution and (3-Trimethoxysilylpropyl)methacrylate (MSPM) treated CNTs were well dispersed in the polymer matrix and improved the properties of PS in the presence of elastomer. In the second part, PS was synthesized with the bulk polymerization method at 0.01, 0.008, and 0.005 mol/L initiator concentrations. The chemical structure, melt flow index, average molecular weights, and thermal properties were used to compare the properties of synthesized PS with commercial PS. The results showed that PS was successfully synthesized with all initiator concentrations, but the properties were close to that of commercial PS at 0.005 mol/L initiator concentration. In the third part, PS-CNT masterbatches were produced with in-situ polymerization at 0.005 mol/L initiator concentration and then characterized in terms of their chemical structure and thermal properties. PS-CNT masterbatches were successfully synthesized with unmodified CNTs, and MSPM treated CNTs. In the fourth part, to investigate the effect of composite preparation techniques on the mechanical, electrical, and shape memory properties, polymer layers of the multilayer composites were prepared using the methods of direct melt mixing and dilution of PS-CNTs masterbatches. Based on the results, the composite produced with the masterbatch dilution method containing MSPM-CNTs had 33% higher tensile strength and 34% higher tensile modulus than the sample fabricated with the direct melt mixing. The fifth part of the thesis aimed to improve the interfacial adhesion between the layers of the multilayer composites by modifying the CFs with a silane coupling agent, a copolymer, PS-based coatings, and forming nanofibers with the electrospinning of polyamide 6. Among all the modification techniques applied to the CFs, the highest peel strength was obtained in CFRP containing MSPM modified CF as the value of 1962 N/m, which was 21% higher than as-received CF. In the final part of the thesis, multilayer composites were fabricated with one, three, and five CF layers. A five-layered sample was also prepared with MSPM treated CFs (MSPM-CFs) to observe the surface treatment effect on the improvement of interfacial adhesion between the composite layers. The composites were characterized by morphology, mechanical, electrical, thermal, and shape memory properties. Increasing the number of CF layers from one to five, tensile strength, tensile modulus, and electrical resistivity were improved by 527%, 125%, and 70%, respectively. More homogeneous impregnation of polymeric material through the fibers was obtained in the multilayer composite fabricated with MSPM-CFs. Electrically triggered shape recovery of all the multilayer composites was achieved 100% within one minute.

Subject Keywords

Shape Memory Properties., In-situ Polymerization, Surface Treatment, Carbon Nanotubes, Carbon Fabric-Reinforced Polymers (CFRP)

URI

https://hdl.handle.net/11511/89665

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Graduate School of Natural and Applied Sciences, Thesis